Securities (Details 1) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Amortized cost
Due in one year or less, amortized cost
Due after one year through five years, amortized cost
Due after five years through ten years, amortized cost	139,078
Due after ten years Due after ten years through fifteen years, amortized cost	94,327
Mortgage-related securities	363,512
Total amortized cost	597,017	566,509
Fair value
Due in one year or less, fair value
Due after one year through five years, fair value
Due after five years through ten years, fair value	140,879
Due after ten years Due after ten years through fifteen years, fair value	94,270
Mortgage-related securities	366,620
Total fair value	$ 602,107	$ 574,562